Multiple interactions and complex viscosity: The impact of frequency rheology for the development of high concentration protein formulations

Clinical doses of therapeutic proteins range up to 2 mg/kg bodyweigth per patient and even higher. For patient convenience and competitiveness, subcutaneous (s.c.) applications are required. Therefore, liquid formulations for s.c. applications can reach concentrations of up to 200 mg/ml. One key parameter for the development of biotherapeutics as high concentrated liquid formulations (HCLF) is viscosity. Consequently, high solution viscosity is challenging due to e.g. impeded syringeablitiy and injectability that directly link to patient inconvenience, and high shear stress that potentially impair protein inherent stability. Following Jezek et al. 2011, we consider protein concentrations of \u3e100 mg/ml as “highly concentrated”. During early phases in development of biopharmaceutics only limited material is available. Therefore, prediction of the solution viscosity at higher concentrations (e.g. for HCLF conditions), if required, will be of great benefit. In this study, we applied different approaches comprehensively investigating parameters describing protein-protein interaction, protein hydration, protein conformation at different concentrations, and the volume fraction of the protein molecule in solution. At a molecular level, Protein-Protein Interaction (PPI) are a result of electrostatic-interaction, van-der-Waal (vdW)-forces and hydrophobic forces of bi- or multimodal interaction as well as protein-excipients interaction. At the macroscopic level, these parameters describe a crucial influence on the protein-stability and its rheological behavior in solution. However, during formulation development commonly evaluated PPI parameter such as the second virial coefficient (B22), and/or the concentration- dependent diffusion coefficient (kD). These parameters only describe interactions in dilute conditions, which poses limitations in predicting interactions at high protein concentrations. At dilute conditions, mostly electrostatic double layer repulsion and charge-shielding effects of buffer and excipients components dominate. In contrast, at high concentration, distances between individual molecules are narrowed, and thus attractive forces such as vdW interactions are predominantly present. Therefore, a direct correlation of PPI parameter obtained from dilute to crowded conditions is only a shaky compromise. The mechanisms and principles driving the formation of highly viscose systems are not fully understood, especially at the molecular level. As a consequence, the attempts to reduce viscosity are often left to chance. In a case study, we evaluated the behaviour of concentrated protein formulations under high-frequency shear excitation in the MHz range. As a result, we propose an explanation for interaction potentials between individual protein molecules linked to high solution viscosity by extending the complex colloid theory. Multiple attraction forces result in a complex viscous behavior, the formation of a transient micro-rheological network of multiple interacting protein molecules, and the formation of an elastic modulus. In order to lower the viscosity, such multiple interactions have to be disrupted and disordered by different excipients. However, the interaction potential is correlated to the characteristics of each mAb molecule and can be altered by excipients in a defined way. By relating low concentration PPI measurements and wet-lab determined molecular characteristics (e.g. effective surface charge, dipole moment) it is possible to predicts the potency for describing a high viscosity for each mAb. Knowing the effects of pH and different buffer and excipients, a guided development for decreasing the viscosity by different excipients and formulation conditions is possible. High frequency rheology allows a rapid and early evaluation of the viscosity properties of early candidates and thus support subsequent formulation development

Activation energies define kinetic (in)stabilities of therapeutic antibodies

Antibody degradation pathways are many-fold and can result in loss of function, efficacy and even to adverse effects in patients. Among others, aggregation and fragmentation is still the major challenge. The identification of the primary degradation pathway can be very complex. Monoclonal antibodies (mAbs) are large, multi-domain macromolecules. Due to their complex nature and inherent properties, temperature induced unfolding leads to rather complex unfolding kinetics. In this study, we determined activation energies (Ea) of thermal intrinsic fluorescence (IF) unfolding profiles unique for each individual antibody. The analyzed activation energies give insights both into kinetic (in)stabilities of single domains and the overall structure of the antibody. To realize this, we used a novel developed experimental setup to perform temperature dependent fluorescence unfolding profiles of various mAbs. In conclusion, the activation energies can be used as descriptors for kinetic (in)stabilities of therapeutic antibodies. Moreover, we show that lower activation energies correlate to monomer loss in long-term storage stabilities and can thus likely be used for shelf-life prediction

Physicochemical characterization of the endotoxins from Coxiella burnetii strain Priscilla in relation to their bioactivities

BACKGROUND: Coxiella burnetii is the etiological agent of Q fever found worldwide. The microorganism has like other Gram-negative bacteria a lipopolysaccharide (LPS, endotoxin) in its outer membrane, which is important for the pathogenicity of the bacteria. In order to understand the biological activity of LPS, a detailed physico-chemical analysis of LPS is of utmost importace. RESULTS: The lipid A moiety of LPS is tetraacylated and has longer (C-16) acyl chains than most other lipid A from enterobacterial strains. The two ester-linked 3-OH fatty acids found in the latter are lacking. The acyl chains of the C. burnetii endotoxins exhibit a broad melting range between 5 and 25°C for LPS and 10 and 40°C for lipid A. The lipid A moiety has a cubic inverted aggregate structure, and the inclination angle of the D-glucosamine disaccharide backbone plane of the lipid A part with respect to the membrane normal is around 40°. Furthermore, the endotoxins readily intercalate into phospholipid liposomes mediated by the lipopolysaccharide-binding protein (LBP). The endotoxin-induced tumor necrosis factor α (TNFα) production in human mononuclear cells is one order of magnitude lower than that found for endotoxins from enterobacterial strains, whereas the same activity as in the latter compounds is found in the clotting reaction of the Limulus amebocyte lysate assay. CONCLUSIONS: Despite a considerably different chemical primary structure of the C. burnetii lipid A in comparison with enterobacterial lipid A, the data can be well understood by applying the previously presented conformational concept of endotoxicity, a conical shape of the lipid A moiety of LPS and a sufficiently high inclination of the sugar backbone plane with respect to the membrane plane. Importantly, the role of the acyl chain fluidity in modulating endotoxicity now becomes more evident

Biophysical Mechanisms of the Neutralization of Endotoxins by Lipopolyamines

Endotoxins (lipopolysaccharides, LPS) are one of the strongest immunostimulators in nature, responsible for beneficial effects at low, and pathophysiological effects at high concentrations, the latter frequently leading to sepsis and septic shock associated with high mortality in critical care settings. There are no drugs specifically targeting the pathophysiology of sepsis, and new therapeutic agents are therefore urgently needed. The lipopolyamines are a novel class of small molecules designed to sequester and neutralize LPS. To understand the mechanisms underlying the binding and neutralization of LPS toxicity, we have performed detailed biophysical analyses of the interactions of LPS with candidate lipopolyamines which differ in their potencies of LPS neutralization. We examined gel-to-liquid crystalline phase behavior of LPS and of its supramolecular aggregate structures in the absence and presence of lipopolyamines, the ability of such compounds to incorporate into different membrane systems, and the thermodynamics of the LPS:lipopolyamine binding. We have found that the mechanisms which govern the inactivation process of LPS obey similar rules as found for other active endotoxin neutralizers such as certain antimicrobial peptides

Divalent cations affect chain mobility and aggregate structure of lipopolysaccharide from Salmonella minnesota reflected in a decrease of its biological activity

AbstractThe physicochemical properties and biological activities of rough mutant lipopolysaccharides Re (LPS Re) as preformed divalent cation (Mg2+, Ca2+, Ba2+) salt form or as natural or triethylamine (Ten+)-salt form under the influence of externally added divalent cations were investigated using complementary methods: Differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopic (FT-IR) measurements for the β↔α gel to liquid crystalline phase behaviour of the acyl chains of LPS, synchrotron radiation X-ray diffraction studies for their aggregate structures, electron density calculations of the LPS bilayer systems, and LPS-induced cytokine (interleukin-6) production in human mononuclear cells. The divalent cation salt forms of LPS exhibit considerable changes in physicochemical parameters such as acyl chain mobility and aggregate structures as compared to the natural or monovalent cation salt forms. Concomitantly, the biological activity was much lower in particular for the Ca2+- and Ba2+-salt forms. This decrease in activity results mainly from the conversion of the unilamellar/cubic aggregate structure of LPS into a multilamellar one. The reduced activity also clearly correlates with the higher order – lower mobility – of the lipid A acyl chains. Both effects can be understood by an impediment of the interactions of LPS with binding proteins such as lipopolysaccharide-binding protein (LBP) and CD14 due to the action of the divalent cations

Strategies for the Assessment of Protein Aggregates in Pharmaceutical Biotech Product Development

Within the European Immunogenicity Platform (EIP) (http://www.e-i-p.eu), the Protein Characterization Subcommittee (EIP-PCS) has been established to discuss and exchange experience of protein characterization in relation to unwanted immunogenicity. In this commentary, we, as representatives of EIP-PCS, review the current state of methods for analysis of protein aggregates. Moreover, we elaborate on why these methods should be used during product development and make recommendations to the biotech community with regard to strategies for their application during the development of protein therapeutics

Thermodynamic analysis of the lipopolysaccharide-dependent resistance of gram-negative bacteria against polymyxin B

Cationic antimicrobial cationic peptides (CAMP) have been found in recent years to play a decisive role in hosts' defense against microbial infection. They have also been investigated as a new therapeutic tool, necessary in particular due to the increasing resistance of microbiological populations to antibiotics. The structural basis of the activity of CAMPs has only partly been elucidated and may comprise quite different mechanism at the site of the bacterial cell membranes or in their cytoplasm. Polymyxin B (PMB) is a CAMP which is effective in particular against Gram-negative bacteria and has been well studied with the aim to understand its interaction with the outer membrane or isolated membrane components such as lipopolysaccharide (LPS) and to de. ne the mechanism by which the peptides kill bacteria or neutralize LPS. Since PMB resistance of bacteria is a long-known phenomenon and is attributed to structural changes in the LPS moiety of the respective bacteria, we have performed a thermodynamic and biophysical analysis to get insights into the mechanisms of various LPS/PMB interactions in comparison to LPS from sensitive strains. In isothermal titration calorimetric (ITC) experiments considerable differences of PMB binding to sensitive and resistant LPS were found. For sensitive LPS the endothermic enthalpy change in the gel phase of the hydrocarbon chains converts into an exothermic reaction in the liquid crystalline phase. In contrast, for resistant LPS the binding enthalpy change remains endothermic in both phases. As infrared data show, these differences can be explained by steric changes in the headgroup region of the respective LPS

ДОСЛІДЖЕННЯ ЕКОНОМІЧНОЇ ПРИРОДИ АМОРТИЗАЦІЇ

В статті досліджується амортизація як економічна категорія і реальний процес господарської діяльності підприємств. Виділені основні проблеми, що виникають під час її обліку та стоять на заваді використання амортизації як джерела нагромадження основного капіталу. Запропоновано напрямки перетворення її у власне інвестиційне джерело підприємств. Depreciation as an economic category and real process of enterprises’ activity are investigated in the article. The author determines the main problems, which are the obstacles for depreciation’s calculating as well as using it as the source of the fixed capital accumulation, and suggests the ways of transformation it into own investment source of the enterprises

Bacterial cell wall compounds as promising targets of antimicrobial agents I. Antimicrobial peptides and lipopolyamines

The first barrier that an antimicrobial agent must overcome when interacting with its target is the microbial cell wall. In the case of Gram-negative bacteria, additional to the cytoplasmic membrane and the peptidoglycan layer, an outer membrane (OM) is the outermost barrier. The OM has an asymmetric distribution of the lipids with phospholipids and lipopolysaccharide (LPS) located in the inner and outer leaflets, respectively. In contrast, Gram-positive bacteria lack OM and possess a much thicker peptidoglycan layer compared to their Gram-negative counterparts. An additional class of amphiphiles exists in Gram-positives, the lipoteichoic acids (LTA), which may represent important structural components. These long molecules cross-bridge the entire cell envelope with their lipid component inserting into the outer leaflet of the cytoplasmic membrane and the teichoic acid portion penetrating into the peptidoglycan layer. Furthermore, both classes of bacteria have other important amphiphiles, such as lipoproteins, whose importance has become evident only recently. It is not known yet whether any of these amphiphilic components are able to stimulate the immune system under physiological conditions as constituents of intact bacteria. However, all of them have a very high pro-inflammatory activity when released from the cell. Such a release may take place through the interaction with the immune system, or with antibiotics (particularly with those targeting cell wall components), or simply by the bacterial division. Therefore, a given antimicrobial agent must ideally have a double character, namely, it must overcome the bacterial cell wall barrier, without inducing the liberation of the pro-inflammatory amphiphiles. Here, new data are presented which describe the development and use of membrane-active antimicrobial agents, in particular antimicrobial peptides (AMPs) and lipopolyamines. In this way, essential progress was achieved, in particular with respect to the inhibition of deleterious consequences of bacterial infections such as severe sepsis and septic shock